Three-phase electric furnace



F. T. SNYDER.

- THREE-PHASE ELECTRIC FURNACE.

APPLICATION FILED MAR. H. 1918.

Patented Jan. 6, 1920.

2 SHEETSSHEE I.

j]; W 10 V F ZW V F. T. SNYDER.

Patented Jan. 6, 1920.

2 SHEETSSHEET 2.

W 5566- J5 jzaz/emfor D 1' W G W UNITED STATES OFFICE.

FREDERICK T. SNYDER, 0F OAK PARK, ILLINOIS, ASSIGNOR TO INDUSTRIAL ELECTRIC FURNACE COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF INDIANA.

THREE-PHASE ELECTRIC FURNACE.

Specification of Letters Patent.

Patented J an. 6, 1920.

Application filed March 11, 1918. Serial No. 221,610.

To all whom it may concern:

Be it known that I. FREDERICK T. SNY- maa, a citizen of the United States, residing at Oak Park, in the county of Cook and State of Illinois, have invented a certain new and useful Improvement in Three-Phase Electric Furnaces, of which the following is a full, clear, concise, and exact description.

My invention relates to improvements in electric furnaces of the multi-phase current type and to the method of operating the same.

It has been customary heretofore to operate a three phase electric furnace with three carbon electrodes which extend into the furnace from the roof thereof. Each electrode consumed during the operation of an electric furnace, however, constitutes an additional source of expense and for this reason it is desirable to reduce the number of electrodes employed as far as consistent with the other factors to be Considered. Attempts have been made in the past to reduce the number of upper electrodes to two, using one bottom contact. For this purpose, however, it has been necessary to use current in a two phase" circuit and transform it from-three phase current before it is supplied to the furnace. It is also necessary in such cases to employ special transformers, these transformers constituting an additional item of expense.

The object of the present invention is to provide an improved method and means whereby three phase supply current may be applied to an electric furnace having only two carbon electrodes and a bottom contact. In carrying out my invention therefor, I am enabled not only to dispense with the third carbon electrode constituting an item of additional expense, but I am enabled to use three standard transformers, all of which are .alike, thereby effecting a further economy. In my copending application, Serial No. 221,609 also filed March 11th, 1918, I have disclosed other means and a method for operating an electric furnace of this character directly from a three phase circuit.

In the accompanying drawings I have illustrated diagrammatically tWo embodiments of the/invention.

Figure 1 is a diagram of the complete circuit connections including the furnace, in one form of the inventio Fig. 2 is a simplified diagram of the transformer connections, showing the phase relations. I

Fig. 3 is a diagram of another form of the invention, and

Fig. 1 is a simplified diagram of the transformer connections thereof, showing the phase relations.

In diagrams Figs. 1 and 2, 1 represents the electric furnace, which is provided with two adjustable carbon electrodes 2 and 3 projecting through the roof thereof and with a metallic bottom contact 4.

Three transformers 5, 6 and 7 are employed, which are connected to "the three foregoing terminals. These transformers may be of standard construction. Such construction customarilyprovides that the secondary windings are arranged in two groups of coils, with the terminals brought up to a connection board near the top of the oil bath. The primary windings 8, 9 and 10 of these transformers are connected preferably in delta across the mains 11, 12 and 13 of a three phase alternating current circu it. This delta connection is not eential, as the equivalent star connectionmay be substituted, although it has been found in practice that the delta connection serves to maintain a. better balance on the primary circuit when the load fluctuates between the different arcs.

- The secondary windings of the transformers each consist of two coils 14 --14, 15-15 and 1616. These secondary windings may be connected in star as shown par-,

ticularly in Fig. 2, in which the angles and.

position of the terminals are drawn to illus trate the phase relations. Two of the ends of said star are connected to the two upper movable carbon electrodes of the: furnace.

in parallel with each other.

There are three electrical loads in the furnace which are carried respectively by one of each of the three phases of the power supply. One load represents the energy dethe electrode 3 to the bottom contact 4.

veloped by the are between the carbon electrod 2 and the metallic contact 4:. The Second load is represented by the energy developed by the are between the carbon electrode 3 and the metallic contact 4. The third lo ad'i's representcd by the energy developed by the two arcs in series between the carbon electrodes 2 and 3. As this load comprises two arcs, the resistance of the circuit will be greater than the corresponding resistance in the case of the other two loads. In order to produce an even distribution of the loading on the three phases of the primary current, the voltage represented by this third load must be correspondingly greater in proportion to said larger resistance. Said increased voita e is provided by the arrangement of secondaries in parallel in the transformer which is connected to the bottom contact oft the furnace and by the arrangement of secondaries in series in the transformers which are connected. to the upper electrodes. T his increased voltage results in an increased current flow between the two upper electrodes, whereby said current flow more nearly equals the flow from either electrode to the bottom contact.

In the form of invention shown in Figs. 3. and 4, the secondary coils of the transformers are connected in delta as distinguished from a star connection. The same reference characters have been employed as before to indicate parts previously de scribed.

The transformer 6 has its secondary windings 17-17 connected in series with each other in a circuit which extends from the electrode 2 to the botton'i contact 4. In like manner the transformer 7 has its secondary windings l8l8 connected in series with each other in the circuit that extends from The transformer has its secondaries 19-19 connect-ed one each in each of the two previously mentioned circuits, the terminals of each. coil 19 being reversed in phase in insorting said coils in the circuit of said transformer. These connections are illustrated in simplified form in Fig. 4, in which the angles and position of the terminals are drawn. to illustrate the phase relations. It will be noted that the phase angle DCE is 60 and under these conditions the angle ACE is about 98. If the transformers in Fig. 2 are duplicates in construction and the phase angles between the lines AF, BF and CF are 120 as shown, the voltages between the terminals C, A and C, B will be 82 apart in their phase relation, that is, the angle between the phases of the voltages between the two electrodes and the bottom contact will be, less than 90 and greater than 60.

The invention is not necessarily limited to the details shown and described, as said invention may be embodied in various other forms. For example, a single three phase transformer can be substituted for the three single phase transformers illustrated. It will be understood also that the electric furnace is illustrated diagrammatically and that the structural details in practice are somewhat more elaborate than those shown herein. For example, although the bottom contact at is shown as a single contact, in practice it may be made as a plurality of contacts in parallel in order to carry the required current. The furnace structure is covered by various other applications and is therefore not illustrated fully herein,

Various changes may be made from what is disclosed herein without departing from the spirit of the invention as set out in the appended claims.

Having thus described my invention what 1 claim as new and desire to secure by Letters Patent or the United States is:

1. The combination with an electric furnace having two upper electrodes and a bottom contact, of three transformers, the secondaries of which are so connected as to produce a phase angle between the voltages existing between the bottom contact and said upper electrodes, greater than 60 and less than 90.

2. The combination with an electric furnace having two upper electrodes and a bottom contact, of three transformers, the secondaries of which are so connected as to produce a phase angle between the voltages existing between the bottom contact and said upper electrodes, less than 90 while producing a voltage between the upper electrodes greater than either voltage between the electrodes and said bottom contact.

3. The combination with an electric furnace having two upper electrodes and a bottom contact, of three transformers having their primary windings connected to a three phase circuit and having their secondary windings arranged in a star connection, two ends of said star being connected. to said two upper electrodes respectively and the third endof said star being connected with said bottom contact.

l. The combination with an electric furnace having two adjustable upper electrodes and a bottom contact, of threesimilar transformers having their primary windin s connected in delta to a three phase circuit and having their secondary windings arranged in astar connection, two ends of said star being connected to said two upper electroges respectively and the third end of sai star being. connected with said bottom contact, each secondary winding consisting of two coils, the pairs of coils of the secondary winding connected to said bottom contact being in parallel with each other and the pairs of coils of each of the remainin secondary windings being in series with each other.

5. In a three phase electric furnace, a source of three phase alternating current, three transformers having their primaries connected with said source of current and having their secondaries consisting of a plurality of coils, the coils of two of said secondaries being connected in series, the coils of the third secondary being connected in parallel, to provide for an even distribution of the loading.

6. In combination, an electric furnace and three transformers each having secondary windings in two coils, said secondary windings of said three transformers being con- I nected in star, the two secondary coils in two of the transformers being connected in series and the two secondary coils of the tllllll'ld transformer being connected in para e.

7. The combination with aithree phase electric furnace of a source of three phase alternating current, three transformers hav ing their primaries connected with said source of current and having their secondaries consisting of a plurality of coils, said coils being partly in series and partly in parallel with each other to provide for an even distribution of the loading.

In witness whereof, I hereunto subscribe my name this ninth day of March A. D.,

FREDERICK T. SNYDER. 

